7.3 IDI injection pump removal and compression testing after the fact.

[stick_witch]

Hey guys! So I've got my truck in the shop to fix some oil leaks and to replace my leaking injection pump and I got overly excited and took off the IP and disconnected the hard lines running to and from the fuel filter head without doing my compression tests on the cylinders of this new to me rig, and in turn made a lot more work for myself now.

I would really like to do a compression test before I go and send the pump off to be rebuilt, so I'm wondering if this can be done without spraying diesel out of the lift pump and without messing up timing on the IP when I go to put it back in (its my understanding that the pump only goes into the timing gear one way so even if it turns without the pump in it, it shouldn't matter, right?) and if so how can it be done? Is there anything I should be cautious about when doing the compression test? I have the injectors still in but no hard lines or return lines connected. Planning on using a diesel specific compression gauge with a 10x1.0mm glowplug adapter. I sorta get the gist, but not sure how it will affect my motor turning it over with no IP in it.

Truck in question is the 1989 F250 detailed in my signature.

 

[The_Josh_Bear]

That's a good question, it all depends on if the timing gear is held in place by the cover or requires the pump to be installed. Which I don't know, unfortunately. But it seems to me the pump would need to be installed.

*If* the cover holds the gear then just take a hose and bucket for the lift pump fuel so that's taken care of, then pull all 8 GP's and have charged up batteries before giving it a whirl.

 

[stick_witch]

That's a good question, it all depends on if the timing gear is held in place by the cover or requires the pump to be installed. Which I don't know, unfortunately. But it seems to me the pump would need to be installed.

*If* the cover holds the gear then just take a hose and bucket for the lift pump fuel so that's taken care of, then pull all 8 GP's and have charged up batteries before giving it a whirl.

Yeah, I would think that the timing gear must be held in by the cover itself, otherwise it would just float in there and I’d imagine the gear would jump or skip when you try to rattle the IP out of it. But of course I wouldn’t bet my engine on it...

 

[stick_witch]

Yeah, I would think that the timing gear must be held in by the cover itself, otherwise it would just float in there and I’d imagine the gear would jump or skip when you try to rattle the IP out of it. But of course I wouldn’t bet my engine on it...

Correction, after looking at pictures of the IP timing gear and the cover, it appears that the gear is in fact held on axis by the IP. All the cover does when the pump is off is restrict the gear’s clearance so that it doesn’t jump gears. So I definitely won’t be cranking it over without the pump in...

Some pictures below

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[dgr]

Install the pump. Tighten the nuts and bolts. Don't connect the wire to the pump. No diesel is going to spray anywhere.

I would always disconnect the wire when testing. A diesel is going to fire and your going to be buying a new gauge if you don't.

 

[stick_witch]

Install the pump. Tighten the nuts and bolts. Don't connect the wire to the pump. No diesel is going to spray anywhere.

I would always disconnect the wire when testing. A diesel is going to fire and your going to be buying a new gauge if you don't.

Thanks for the heads up! Any other ways to screw up a nice gauge? Im borrowing my friend’s $400 diesel specific snap on gauge...
And yeah, I’m gonna put the pump back in tomorrow just to act as a place holder for the IP timing gear, which should be much easier now with the injector line “spider” taken off, and then I’ll also leave the feed lines to and from the wix filter off and just tape a ziplock over the end to catch any fuel that the lift pump manages to spit out and just pray for some good readings. Its hard to say at 180000, for some it seems its end of the road, and then for others their idi’s are just getting broken in.

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[dgr]

If you don't release the pressure in the gauge before you remove it from the glow plug adapter, you'll blow out the o-ring on the end of the hose. That's the only other gotcha I can think of.

 

[IDIBRONCO]

Since you can have the engine on an engine stand, remove the IP, and then turn the engine upside down without the IP gear skipping a tooth, I don't think that could happen by cranking the engine over with the IP removed. The gear may bounce around and gouge the housing so I would recommend only trying a compression test with the IP installed. When the IP is removed from the housing, the timing will be changed unless you mark the IP and the housing to get them correctly aligned. As for the fuel coming out of the lift pump, just disconnect the rubber hose that goes between the lift pump and the steel line on the frame. Some fuel will still squirt out, but it won't be much.

 

[stick_witch]

Thanks for the help you guys! I did the test. A good easy way to find an answer to the question I posed of if the IP gear just floats under the cover or not is to just put pressure on the gear in the case with your finger, it'll move... lol, so theres the answer.

As far as the test, I just stuck the IP back on without any of the fuel lines and snug down the bolts, put the inspection cover back on, and then as far as the lift pump I just put a ziplock over the hard line that runs up from it to the filter... wish I just disconnected the rubber hose running to the lift pump because it literally filled my large ziplock after testing just 1-2 cylinders, then I'd have to empty it back into the tank. But, nonetheless, it did the job.

As far as the results of the test I was a little thrown off. It took quite a number of compression strokes to get to the peak psi on each cylinder... like 21 strokes... the #s were 380, 380, 340, 340, 380, 290, 440, 420 psi at 21 strokes... yes 21 strokes... is that normal? Should only take like 5-10 strokes, right? Sounds to me like I might have a rebuild in my near future...

 

[hacked89]

Yea 5-10 strokes when I compression test mine I see it peak in about 7-8.

You have an issue in your head or chamber on your 290 cylinder.

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[stick_witch]

Yea 5-10 strokes when I compression test mine I see it peak in about 7-8.

You have an issue in your head or chamber on your 290 cylinder.

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Yeah thats what I though... ooof may have gotten myself a lemon...